Apple agreed to acquire NeXT and its technology in order to bring back Jobs, when Apple was on the cusp of bankruptcy, was absolutely certain to die, and had no negotiating power. It wasn't a merger.
Also modern Apple devices are based on the NeXT's operating system and have nothing other than cosmetic and emulative compatibility with MacOS. OSX/macOS is NeXTStep on top of Mach.
source: bought $100,000 of APPL in 1997.